http://www.archives.gov/publications/prologue/2005/spring/piece-lee.html
On May 29, 1865, President Andrew Johnson issued a Proclamation of Amnesty and Pardon to persons who had participated in the rebellion against the United States. There were fourteen excepted classes, though, and members of those classes had to make special application to the President.
Lee sent an application to Grant and wrote to President Johnson on June 13, 1865:
Being excluded from the provisions of amnesty & pardon contained in the proclamation of the 29th Ulto; I hereby apply for the benefits, & full restoration of all rights & privileges extended to those included in its terms. I graduated at the Mil. Academy at West Point in June 1829. Resigned from the U.S. Army April '61. Was a General in the Confederate Army, & included in the surrender of the Army of N. Va. 9 April '65.
Larger Version Lee signed his Amnesty Oath on October 2, 1865, but was not restored to full citizenship in his lifetime. (General Records of the Department of State, RG 59)
On October 2, 1865, the same day that Lee was inaugurated as president of Washington College in Lexington, Virginia, he signed his Amnesty Oath, thereby complying fully with the provision of Johnson's proclamation. But Lee was not pardoned, nor was his citizenship restored. And the fact that he had submitted an amnesty oath at all was soon lost to history.
More than a hundred years later, in 1970, an archivist at the National Archives discovered Lee's Amnesty Oath among State Department records (reported in Prologue, Winter 1970). Apparently Secretary of State William H. Seward had given Lee's application to a friend as a souvenir, and the State Department had pigeonholed the oath.
In 1975, Lee's full rights of citizenship were posthumously restored by a joint congressional resolution effective June 13, 1865.